Frequency discriminator circuits



Aug. '30, 1949. E. L. c. WHITE 2,430,799

' FREQUENCY DISCRIMINATOR CIRCUITS Original Filed March 5, 1945KLKS'TKON Z4 5 r0 our/ ar Q 22 SOURCE IL S \1 r0 sou/ac:- 0F 60/77/704tZ'CT/fifl' 39 P07E/V7/4L INVENTOR 56c 1. C W/wrz ATTORNEY Patented Aug.30, 1949 UNITED STATES 2,480,799 FREQUENCY DISCRIMINATOR CIRCUITS EricLawrence Casling White, St. Boniface, Richings Way, 'Iver, England,assignor to Electric & Musical Industries Limited, Hayes, Middlesex,England, a company of Great Britain Original application March 3, 1945,Serial N0.

580,821. Divided and this application November 14, 1945,' Serial No.628,564. In Great Britain March 25, 1944 Section 1, Public Law 690,August 8, 1946 Patent expires March 25, 1964 The object of the presentinvention is to provide an improved frequency discriminator circuit foruse with oscillations of very high frequency having a wave-length of theorder of centimeters.

According to the present invention a frequency discriminator circuit foruse with oscillations of very high frequency is provided, and comprisesa velocity modulation electron discharge valve arrangement including twooutput resonators tuned to different frequencies and arranged to beexcited by applied signals, said resonators being associated with adetector circuit for afiording a differential output which varies as thefrequency of said signals departs from the mean value of the frequenciesto which the resonators are tuned. In order that the invention may beclearly understood and readily carried into-effect, the invention willnow be described more in detail with reference to the accompanyingdiagrammatic drawing which illustrates a frequency discriminator circuitaccording to the invention.

The circuit shown in the drawin comprises a pair of Klystron valves Iand 2 respectivel The valve l comprises an input resonator 3 of toroidalform which serves as a buncher for velocity modulating a stream ofelectrons projecting axially of the resonator between cathode 4 andanode 5. The modulated stream of electrons passes axially of a furtherresonator 6 similar to the resonator 3, and forms the catcher or outputresonator of the valve. The valve 2 is similar to the valve 1, andcomprises a cathode I anode l5. buncher l3, and catcher It.

The bunchers 3 and It may be excited in any suitable way; for example byfrequency modulated oscillations or waves collected by an aerial ll,shown as a dipole, and fed to the bunchers through coaxial conductortransmission lines la. The bunchers 3 and I3 are excited at the samefrequency so that the electron streams in both valves are modulated atthe same frequency, whereby the catchers or output resonators 6 and itare likewise excited at the same frequency. The bunchers 3 and I3 arepreferably tuned to the frequency of excitation, but, according to theinvention, the catchers 6 and l 6 are tuned respectively to frequenciesabove and below the frequency at which they are excited so that theoutputs obtainable from the resonators will vary in opposite senses asthe frequency of excitation ap- I preaches or recedes from the frequencyatwhich either catcher is tuned. The toroidal hollow resonators 3, 6, l3and Hi each has the usual humped characteristic of a conventional tunedcircuit.

The output from the catchert of the valve 1 is fed through a section 20of coaxial conductor transmission line to a rectifier, constituted by acrystal detector 2 I, which is connected on one side througha capacitor22 and a lead connected to the end closure of thetransmission linesection 2Ei'to the mid-point of a load impedance 23, and through a choke24 to one end of the load-impedance 23 and at its other side via thecentral conductor 25 of the transmissionline section 29 to a loop 26disposed within thebuncher for pick-'- in up energy when thebunch'erisexcited. The transmission line section 20'has a length effectivelyequal to a quarter of a wavelength at the frequency of excitation, sothat variations in the impedance in the crystal detector do not afiectthe tuning of the resonatorfig The catcher it of the valve 2, has anoutput circuit similar to that ofthe catcher 5 of the valve l andincludes a section of jcoaxial conductor transmission line 30, crystaldetector 3|, capacitor 32, choke 34 and the half of the load impedance23 not included in the output circuit of valve I. With this arrangementthe outputs from the two catchers 6 and I6, rectified by the detectors2| and Si respectively, will be combined differentially in the loadimpedance, thus affording a rectified output of which the magnitude andsense will depend on that of the departure of the frequency ofexcitation of the catchers 6 and Hi from the mean of the frequency atwhich the two catchers are tuned.

An arrangement according to the invention may be employed for detectingand reducing frequency variations, for example in the manner describedin my above identified application, Serial No. 580,821. It may, also, beused for detecting frequency modulation of received oscillations, and inthis case the output appearing across the load impedance 23 will be thedesired modulation output, and may be applied with, or withoutamplification to actuate suitable reproduction apparatus, or may be usedfor other purposes. It will be appreciated that the tuning of theresonators 3, 6, l3, and I6 may be effected in any suitable manner.

While the invention has been described in detail as embodied in anarrangement including two separate valves, it will be appreciated that,if desired, a single valve having two catchers arranged for example soas to be excited in turn by the velocity modulated electron stream andtuned to frequencies respectively above and below the frequency ofexcitation, could be employed. With such an arrangement it would benecessary to adjust the impedance in the output circuits of the catchersto insure that the outputs balance atthe desired frequency.

In the drawing, the valves i and 2 are shown as having controlelectrodes 21 and 31 respectively which may be arranged to havepotentials applied to them for causing anode current to fiow in thevalves, or for stopping the flow of such current so as to switch thevalves on and off as required. The means for energizing the electrodesand resonators of tubes 1 and 2 are as shown in Fig. 2 of my aforesaidparent application. Thus, 40 and 4| denotes sources of potential, eachbeing shunted by a respective potentiometer 38 and 39. Each of cathode 4and I4 is connected to the respective negative end of potentiometers 38and 39. The resonators 3 and 6 of tube I are connected to respectivepositive tapping points of potentiometer 38, and resonators l3 and iiiare connected to respective positive tapping points on potentiometer 39.Each of collecting electrodes and I5 is connected to a respectivetapping point on its potentiometer 38 and 39 which is less positive thanthe tapping points of resonators B and IS. The control electrodes 21 and31 are schematically indicated as connected to a common source ofcontrol potential, as explained previously.

What I .claim is:

1. In a circuit for detecting frequency-variable oscillations of veryhigh frequency, means providing a pair of electron streams, a first pairof cavity resonators respectively arranged to excite the respectivestreams, means for exciting the resonators with said oscillations, asecond pair of cavity resonators respectivelyarranged to be excited bysaid streams, said first pair of resonators being tuned in common to thefrequency of the exciting oscillations, said second pair of resonatorsbeing tuned respectively to frequencies above and below the frequency atwhich they are excited, means for separately rectifying the outputenergy of said second pair of resonators, and means for deriving fromthe rectified energies the differential voltage thereof.

2. In a circuit as defined in claim 1, separate Klystron tubes includinga respective one of said streams and one resonator of each of saidpairs.

3. In a circuit as defined in claim 1, each of said cavity resonatorsconsisting of a toroidal resonator through which its respective electronstream passes.

4. In a frequency discriminator, a first electron discharge deviceprovided with a pair of toroidal resonators spaced from a cathode, asecond electron discharge device provided with a second pair of toroidalresonators spaced from a second cathode, a source of high frequencysignals, each of said cathodes providing a respective electron streampassing through each pair of resonators in succession, means couplingsaid source to the first resonator of each of said pairs thereby tomodulate the respective electron streams at the signal frequency, thesecond resonators of said pairs being tuned to respective frequencies oneither side of the signal frequency, a separate rectifier circuitcoupled to each second resonator, and means differentially combining therectified outputs of the rectifier circuits.

ERIC LAWRENCE CASLING WHITE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,293,180 Terman Aug. 18, 19422,314,794 Linder Mar. 23, 1943 2,362,209 Litton Nov. '7, 1944 2,379,819Mason July 3, 1945 2,402,421 Lindenblad June 18, 1946 2,413,939 BenwareJan. 7, 1947 2,414,100 Hansen et a1 Jan. 14, 1947 OTHER REFERENCES Hyperand Ultra High Frequency Engineering by Sarbacher and Edson Publ.,Wiley, chapter 17.

